Khan, from the opposition Labour Party, has called for a 5.7 billion pound ($7.4 billion) package for Transport for London (TfL) after commuters deserted public trains and buses during the pandemic.

Khan says in return the government is insisting on higher fares and a raft of other revenue raising mechanisms such as increasing the size of the congestion zone which requires drivers to pay a fee to drive in the city.

“The current mayor of London had effectively bankrupted TfL before coronavirus had even hit,” Johnson, who himself served as mayor of London from 2008 to 2016, told parliament.

“Any expansion of the congestion charge, or any other measure taken to improve the finances of TfL are entirely the responsibility of the bankrupt current mayor of London,” he said, adding that TfL had been left in “robust health” in 2016.

A spokesman for the mayor did not immediately respond to a request for comment. Coronavirus lockdowns have led to a dramatic fall in the number of journeys across London.

London’s population overtook its 1939 record of 8.6 million in 2015 and, under pre-pandemic forecasts, was forecast to top 10 million by around 2030.

Johnson’s government is locked in negotiations with several city mayors over how businesses should be compensated when they are forced to close during lockdowns and how public services can continue.

Khan, who had frozen the cost of single fares, said in an earlier statement that the government’s proposals would deter Londoners from travelling, further damaging any recovery.

Housing Secretary Robert Jenrick said it had “to resolve the fact that the mayor has bankrupted TfL and the Greater London Authority.”

“We’ve already given multiple billions of pounds to him over the last few years to bail him out,” he said. “How do we take this forwards. Well, I’m afraid it can’t keep falling back to the taxpayers of the whole of the United Kingdom.”